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The preceding table may be used to determine the diameter when the circumference or area is known. Thus, the diameter of a circle having an area of 7,200 sq. in. is, approximately, 95 in.

DECIMAL EQUIVALENTS OF PARTS OF ONE INCH.

1-64 .015625 17-64 .265625 33-64 .515625 49-64.765625 .281250 17-32.531250 | 25-32.781250 .296875 35-64.546875 51-64

1-32 .031250 9-32
3-64 .046875 19-64
1-16 .062500
5-64 .078125
3-32 .093750 11-32 .343750 19-32 .593750

5-16 .312500 9-16 .562500

21-64.328125

37-64.578125

.796875

13-16

.812500

53-64.828125

27-32.843750

7-64 .109375 23-64
1-8 .125000
9-64 .140625
5-32.156250

.359375 39-64

.609375

55-64 .859375

11-64 .171875

3-8 .375000 5-8 25-64 .390625 41-64 13-32.406250 21-32 27-64 .421875

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DECIMALS OF A FOOT FOR EACH 1-32 OF AN INCH.

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DECIMALS OF A FOOT FOR EACH 1-32 OF AN INCH.

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GEOMETRICAL DRAWING.

To erect a perpendicular to the line b c at the point a. With a as a center, and any radius, as ab, strike arcs cutting the line at b and c. From band e as centers, and any radius greater than ba, strike arcs intersecting at d. Draw da, which will be perpendicular to b c at a.

To draw a line parallel to a b. At any points a and b, with a radius equal to the required distance between the lines, draw arcs at c and d. The line cd, tangent to the arcs, will be the required parallel. With a as a center, strike an arc cutting the sides of

To bisect the angle ba c.

the angle in b and c. With b and c as centers, and any radius, strike arcs intersecting, as at d. Draw da, the bisector.

To erect a perpendicular at the end of a line. Take a center anywhere above the line, as at b. Strike an arc passing through a and cutting the given line at c. Draw a line through c and b, cutting the arc at d. Draw the line ad, which will be the required perpendicular.

To divide a line into any number of equal parts. Let it be required to divide the line ab into 5 equal parts. Draw any line a d, and point off 5 equal divisions,

as shown. From 5 draw a line to b and draw 4-4, 3-3', etc. parallel to 5b.

To divide a space between two parallel lines or surfaces (for example, the spacing of risers in a stairway). Draw ab

and ce the given distance apart. Then move a scale along them, until as many spaces are included along a d as there are number of divisions required. Mark the points 1, 2, 3, etc., and draw lines through them parallel to a b and c e.

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An inscribed angle has its vertex (as c or d) in the circumference of a circle. Any angle inscribed in a semicircle is a right angle, as a c b, or a db.

To draw a circle through three points not in a straight line, as a, b, and c.

Bisect ab and also b c. The two bisectors will intersect in a point d, which will be the center of the required circle.

To find the center of a circular arc, as a b c, take a point, as b on the curve, and draw ba and b c. Bisect these lines by perpendiculars; the intersec

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To construct a hexagon from a given side. Describe a circle with a radius ab equal to the given side. Draw a diameter as cb. From c and b as centers, and a radius equal to the given side, draw arcs cutting the circle at k, d, f, and e. Connect c, k, f, b, e, and d.

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